Crack the Crossword

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Across
  1. 2. I'm the messenger of the brain, swift and true, Transmitting signals from old to new. I ensure communication continues to flow. What am I?
  2. 3. Born in a lab, not by natural birth, A genetic marvel, of great worth. Cloned from a cell, with a famous name, The world watched in awe, as I came. What famous animal am I?
  3. 6. I am microorganism, but not a bacteria. I have no defined shape, I split and multiply spreading all around. Without legs to walk or eyes to see, In water, I thrive, as small as can be. What am I?
Down
  1. 1. working tirelessly unseen, Producing energy, the cell's engine so keen. With my double membrane and own DNA in tow, I'm essential for life, as many may know. What am I ?
  2. 4. an organ that never stops growing
  3. 5. an organ that rarely develops cancer